All Custom Firmware allows ISO play. Your question is a little odd however, and I don't know if you're actually asking whether there's a way to install CFW without downgrading to 1.50 first....a little clarification would help your cause.

I'm pretty sure you're the same person who asked this very question about 2 days ago, but anyway...

No, you don't have to downgrade to 1.5, any M33 CFW (not GEN, i think) will allow you to run ISOs, and you don't have to downgrade to 1.5 for any of them anymore. Just upgrade to 5.03 OFW, run ChickHEN and use it to run Hellcat's Recovery Flasher v1.60 and use it to flash 5.00m33-6.